Myself wonders if he’d rather say the Divine Liturgy of Saint James with the Antiochians.
I think he’d be a bit surprised to know the Jews still exist - or, come to think of it, that the world still exists. He might be a bit shocked at how much Christianity has changed the world - and how far the Church has spread, both geographically and doctrinally, even creating new, not-even-remotely-Christian religions like Mormonism, Islam, and Unitarian Universalism. And perhaps just a bit disappointed that things got so out of control…
I think he would be especially distressed at the lack of sacraments in some communities, particularly the Eucharist. It’s how Christians from the earliest had a “personal relationship”. No offense to our Protestant brethren, but this ethereal “personal relationship” doesn’t hold a candle to God’s making Himself present. Jesus in the flesh and spirit is a thousand times better than Jesus in the spirit only.
Finally, I think he’d be rather shocked - though not distressed - at the depths of Catholic doctrinal development. That big, huge catechism alone would probably amaze him. (“My, you people certainly have a lot of time to kill, don’t you? And yet, there’s still much of the world that does not know Christ!”)
How do you think St. Peter would respond to the non-Christians of today?